1. Field of the Invention
The present invention relates to water-absorbing acrylic fibers, and more particularly it relates to porous water-absorbing acrylic fibers especially excellent in dyeing, containing a specific water-absorbing resin and having pores only in the inner layer of the fibers.
2. Description of the Prior Art
Since acylic fibers, like other synthetic fibers such as polyamide, polyester, etc. fibers, are lacking in water- and moisture-absorbing abilities, when used as material for underwear, sheeting, sportswear, summer wear, etc. it has been conventional practice in most cases to use them as mixed spun fabrics with cotton, rayon, etc. so that they can be worn comfortably.
Numerous trials have been made to improve the water- and moisture-absorbing abilities of acrylic fibers, but to date none proposed have satisfactory properties.
For example, when producing acrylic fibers composed of a single component by wet-spinning, if the porous structure of the swollen gel filaments is fixed, acrylic fibers showing a water-absorbing ability can be obtained, but they involve intrinsic disadvantages in that the micropores obtained by this method are unstable and will readily disappear in the subsequent drying step or by ironing, resulting in a lowered water-absorbing ability, extremely high absorption of spinning oil and poor color fastness.
Many proposals have been made on methods of producing micropores in the filaments by spinning a spinning solution to which a specified inorganic or organic substance has been added, and thereafter removing the added substance. However, such methods will pose essential problems including pollution of solvent by said substance or aggravation of working environment, complication of the production process such as the recovery of said substance, and therefore such methods cannot be evaluated as industrially advantageous methods.
Several techniques have been also proposed in which water- and moisture-absorbing abilities are given to acrylic fibers by partially hydrolyzing the fibers. However, such fibers having a large amount of carboxyl groups introduced to the fiber surface will show a remarkable decrease in the physical properties and color fastness, and also will not be able to avoid a sticky feel when they have absorbed water. Therefore, such methods are not satisfactory means in practical use.
Under such circumstances, we made an intensive study to eliminate the above-mentioned disadvantages and to provide water absorbing acrylic fibers excellent in practical properties, in an industrially advantageous manner. As a result, we have found that, by compounding a particular water-absorbing resin, it is possible to produce water-absorbing acrylic fibers having practical properties and having no problems in the production process such as spinnerette clogging, filament breakage, filament entanglement, filament fusion, etc. On the basis of this discovery we filed an application as Japanese Patent Publication No. 35286/1982.
However, even this prior application has defects in dyeing peculiar to porous fibers, for example, dyeing unevenness resulting from a fast dyeing speed of the fibers in low temperature regions, necessity of a large quantity of dyes to be used in comparison with ordinary acrylic fibers because of poor color development of the fibers. Therefore, an improvement of the fibers has been demanded from such a viewpoint.